There is a striking similarity between nuclear science and genetic engineering. Molecular biologists, like nuclear physicists before them, are euphoric over their success at deciphering another of nature's secrets. But genetic engineering is not just another scientific accomplishment. Like nuclear physics, it confers on human beings a power for which they are psychologically and morally unprepared. The physicists have already learned this, to their dismay; the biologists, not yet. Indeed, one Nobel laureate has boasted, "We can outdo evolution."

In the face of the infinite complexity of natural systems, the idea that we could improve on the design of nature is not only hubris, it is frightening. In Lewis Thomas' words, we are ignorant "most of all about the enormous, imponderable system of life in which we are embedded as working parts. We do not really understand nature at all." We know that the Earth behaves like an indivisible, delicately tuned mechanism, in which the inanimate environment is strongly conditioned by living things, and vice versa; but we have only begun to decipher the influence of each part on the whole.

For example, we recognize that certain microorganisms convert organic wastes to usable nutrients, and that this recycling process is critical in maintaining the composition of the atmosphere and other conditions favorable to human life and to the web of species that sustain us. But we cannot predict the effects on these vital microorganisms of accelerated evolution, engineered by man, coupled with the accelerated environmental changes now produced by human activities (such as the production of carbon dioxide on a vast scale from fossil fuels, the distribution of novel chemical pollutants around the earth, the large-scale clearing of forests, displacement of biological diversity by a minuscule number of cultivated species, etc.).

Nevertheless, genetic manipulation of microorganisms by recombinant DNA technology has proceeded rapidly and is now a widespread practice. More than 150 genetic engineering firms, mainly oriented toward the design of industrially useful microorganisms, have been formed in the last two years. From their laboratories, microorganisms with properties taken from higher forms of life will inevitably escape into the ecosphere; other engineered forms will eventually be released intentionally into the environment for purposes such as the solubilization of trace metals in mining operations or the digestion of oil spills. We are laying the groundwork for unforeseen evolutionary changes that may create an inhospitable environment for present species.

Certainly, we can find some assurance in nature's resiliency; life has survived environmental upheavals for millions of years. But as conditions have changed, so has the balance of life, with incompatible forms disappearing and new ones arising. The human species has evolved to fit the present ecological conditions. If there were a drastic change in the environment, some forms of life would undoubtedly adapt, but humans, with their many, exacting biological requirements, could not evolve fast enough to become compatible with the new environment.

The gene pool of the Earth, which comprises all living organisms, is a precious, irreplaceable legacy of natural evolution. It is in the truest sense a one-time occurrence and it would be naive to assume that we can manipulate it without harming ourselves. We do not have the infinite wisdom that would be required.

This is a unique moment in history. With the experience of the nuclear weapons threat to draw on, we ought now to be able to act before another crisis is upon us. We ought not to be blinded by the short- term promises of genetic engineering. Unlike pollution and other forms of assault on the environment, once new genetic forms have become established they cannot be "cleaned up." It is not possible to reconstruct an earlier evolutionary era.

Forty years ago, physicists discovered that energy could be unleashed from the atomic nucleus; at the same time, biologists discovered that DNA, the material of the cell nucleus, was the genetic stuff of life. These twin scientific feats, one at the core of matter, the other at the core of life, are without doubt the most momentous discoveries of the 20th century. They demand a new consciousness if human life on this planet is to continue. We have mismanaged the applications of the first discovery. Now, as the second is about to be exploited, we must not permit the biosphere, surpassing as it does our understanding, to become an experimental subject. There is only one Earth, one earthly biosphere, and we are part of it. There is no margin for error.